Sonoluminescence is a well-known phenomena discovered in the 1930's in which light is generated when a liquid is cavitated. Although a variety of techniques for cavitating the liquid are known (e.g., spark discharge, laser pulse, flowing the liquid through a Venturi tube), one of the most common techniques is through the application of high intensity sound waves.
In essence, the cavitation process consists of three stages; bubble formation, growth and subsequent collapse. The bubble or bubbles cavitated during this process absorb the applied energy, for example sound energy, and then release the energy in the form of light emission during an extremely brief period of time. The intensity of the generated light depends on a variety of factors including the physical properties of the liquid (e.g., density, surface tension, vapor pressure, chemical structure, temperature, hydrostatic pressure, etc.) and the applied energy (e.g., sound wave amplitude, sound wave frequency, etc.).
Although it is generally recognized that during the collapse of a cavitating bubble extremely high temperature plasmas are developed, leading to the observed sonoluminescence effect, many aspects of the phenomena have not yet been characterized. As such, the phenomena is at the heart of a considerable amount of research as scientists attempt to not only completely characterize the phenomena (e.g., effects of pressure on the cavitating medium), but also its many applications (e.g., sonochemistry, chemical detoxification, ultrasonic cleaning, etc.).
In a typical cavitation system, for example as shown by Dan et al. in an article entitled Ambient Pressure Effect on Single-Bubble Sonoluminescence (vol. 83, no. 9 of Physical Review Letters), the cavitation chamber is a simple glass flask that is filled or semi-filled with cavitation fluid. A spherical flask is also disclosed in U.S. Pat. No. 5,659,173. The specification of this patent discloses using flasks of Pyrex®, Kontes®, and glass with sizes ranging from 10 milliliters to 5 liters. The drivers as well as a microphone piezoelectric were epoxied to the exterior surface of the chamber.
In some instances, more elaborate chambers are employed in the cavitation system. For example, U.S. Pat. No. 4,333,796 discloses a cavitation chamber designed for use with a liquid metal. As disclosed, the chamber is generally cylindrical and comprised of a refractory metal such as tungsten, titanium, molybdenum, rhenium or some alloy thereof. Surrounding the cavitation chamber is a housing which is purportedly used as a neutron and tritium shield. Projecting through both the outer housing and the cavitation chamber walls are a number of acoustic horns, each of the acoustic horns being coupled to a transducer which supplies the mechanical energy to the associated horn. The specification discloses that the horns, through the use of flanges, are secured to the chamber/housing walls in such a way as to provide a seal and that the transducers are mounted to the outer ends of the horns.
A tube-shaped cavitation system is disclosed in U.S. Pat. No. 5,658,534, the tube fabricated from stainless steel. Multiple ultrasonic transducers are attached to the cavitation tube, each transducer being fixed to a cylindrical half-wavelength coupler by a stud, the coupler being clamped within a stainless steel collar welded to the outside of the sonochemical tube. The collars allow circulation of oil through the collar and an external heat exchanger.
Another tube-shaped cavitation system is disclosed in U.S. Pat. No. 6,361,747. In this cavitation system the acoustic cavitation reactor is comprised of a flexible tube. The liquid to be treated circulates through the tube. Electroacoustic transducers are radially and uniformly distributed around the tube, each of the electroacoustic transducers having a prismatic bar shape. A film of lubricant is interposed between the transducer heads and the wall of the tube to help couple the acoustic energy into the tube.
U.S. Pat. No. 5,858,104 discloses a shock wave chamber partially filled with a liquid. The remaining portion of the chamber is filled with gas which can be pressurized by a connected pressure source. Acoustic transducers are used to position an object within the chamber while another transducer delivers a compressional acoustic shock wave into the liquid. A flexible membrane separating the liquid from the gas reflects the compressional shock wave as a dilation wave focused on the location of the object about which a bubble is formed.
PCT application Ser. No. US02/16761 discloses a nuclear fusion reactor in which at least a portion of the liquid within the reactor is placed into a state of tension, this state of tension being less than the cavitation threshold of the liquid. The liquid preferably includes enriched deuterium or tritium, the inventors citing deuterated acetone as an exemplary liquid. In at least one disclosed embodiment, acoustic waves are used to pretension the liquid. In order to minimize the effects of gas cushioning during bubble implosion, the liquid is degassed prior to tensioning. A resonant cavity is formed within the chamber using upper and lower pistons, the pistons preferably fabricated from glass. The upper and lower pistons are smaller than the inside diameter of the chamber, thus allowing cavitation fluid to pass by the pistons. In a preferred embodiment, the upper piston is flexibly anchored to the chamber using wire anchors while the lower piston is rigidly anchored to the chamber.